The present invention relates to a vibrating screen apparatus. More particularly, the present invention relates to a vibrating screen apparatus capable of maintaining operation when the vibrating apparatus is in an out-of-level orientation.
Vibrating screens for separating particulate matter into various sizes are well known. Particulate matter is typically placed on a screen deck of the vibrating screen. The screen is formed to include a plurality of openings having a predetermined size. Pieces of the particulate matter which are smaller than the predetermined size fall through the openings in the screen deck. Pieces of the particulate matter which are larger than the predetermined size of the openings move across the screen deck to a location separate from the smaller pieces. The vibrating screen decks are typically coupled to a rigid frame. The frame is vibrated by a vibrating mechanism coupled to the frame. Conventional vibrating mechanisms include an eccentric shaft which is rotated within a shaft housing. The lower portion of the shaft housing typically serves as an oil reservoir across its entire length. The oil in the oil reservoir is agitated by oil slingers located on the eccentric shaft. Therefore, oil constantly envelopes spherical roller bearings coupled to the eccentric shaft and all other moving parts located inside the shaft housing. Oil lubrication of the shaft bearings is preferred over grease lubrication. Oil is continuously splashed into the bearings coupled to the shaft of the vibrating mechanism. Bearings lubricated with oil are typically more reliable and have higher dynamic capacities than bearings lubricated with grease.
Several uses have been developed for vibrating screens. One such use is on a movable asphalt pavement recycling apparatus. One such movable asphalt pavement recycling apparatus is described in U.S. Pat. No. 4,946,307. The apparatus described in the '307 patent uses a vibrating screen to separate asphalt particles removed from a road surface by a milling drum. A vertical bucket type conveyor supplies asphalt particles cut from the road by the milling drum to the vibrating screen. Smaller asphalt particles fall through the vibrating screen to a conveyor and are deposited on the road ahead of a resurfacing machine. Larger particles pass over the vibrating screen and are reapplied to the road upstream from the milling drum so that the milling drum grinds the particles into smaller pieces.
Problems arise when operating a vibrating screen on a movable apparatus such as the movable asphalt pavement recycling apparatus discussed above. The road being recycled is typically crowned in the center to promote drainage. This crown can cause an out-of-level condition for the recycling apparatus and for the vibrating screen coupled to the recycling apparatus.
Conventional vibrating mechanisms which are used to vibrate screens include an oil bath incorporated in an eccentric shaft housing which spans the entire width of the vibrating screen frame. If an out-of-level condition occurs in a conventional vibrating mechanism, oil moves toward the lower end of the shaft housing. Therefore, the lower end of the shaft housing has a deeper oil level than the higher end of the shaft housing. This out-of-level condition can cause lubricant starvation of the bearing on the high side of the vibrating mechanism and over-lubrication of the bearing on the low side of the vibrating mechanism. Both lubricant starvation and over-lubrication can damage the bearings coupled to the eccentric drive shaft. When bearings at both ends of the drive shaft share a common oil bath, all the bearings are contaminated and need to be replaced if a single bearing fails.
The vibrating screen apparatus of the present invention includes an improved vibrating mechanism designed to reduce the problems associated with a conventional vibrating mechanism when an out-of-level condition occurs. The vibrating mechanism of the present invention includes a drive shaft, a driven shaft, and two separate oil baths. A first oil bath is located at a first end of the vibrating mechanism adjacent a first pair of bearings coupled to a first end of the drive shaft and the driven shaft. A second oil bath is located at a second end of the vibrating mechanism adjacent a second pair of bearings coupled to a second end of the drive shaft and driven shaft. Therefore, if the vibrating screen apparatus is out-of-level, the depth of the oil in the two oil baths will not change substantially in the limited area of the two oil baths surrounding the bearings. In addition, only two bearings share a common oil bath. Therefore, if bearing failure occurs, only the two bearings that share the common oil bath would be contaminated and need to be replaced.
One feature of the present invention is the provision of oil retention means to prevent the loss of oil and to prevent oil from migrating down the eccentric shaft from one oil bath to the other oil bath through the shaft housing. The vibrating mechanism of the present invention includes internal labyrinth seals configured to prevent oil from passing along the shafts past the seals and out of the oil baths. However, some amount of leakage past the seals is typically present. Oil which passes a labyrinth seal coupled to the shaft is propelled radially outwardly off the shaft by an O-ring coupled to the shaft and into an oil collection pocket formed in the shaft housing. When the oil level in the oil collection pocket rises above a predetermined level, the oil flows through a drain back into the oil bath adjacent the oil collection pocket.
Another feature of the present invention is the provision of rubber shear spring assemblies mounted as side stabilizers on the frame of the vibrating screen. The rubber shear spring assemblies are formed from a flexible rubber element permanently bonded to steel mounting plates on either side of the flexible rubber material. The rubber shear spring assemblies are preferably mounted in a central position behind main support coil springs. The rubber shear spring assemblies are relatively free to oscillate and deflect in shear, which is parallel to the faces of the mounting plates. However, the rubber shear spring assemblies are generally rigid in compression and in tension. Therefore, the rubber shear spring assemblies permit the vibrating frame to move up and down. However, the rubber shear spring assemblies resist sideways movement of the frame when an out-of-level occurs. If the frame begins to shift due to an out-of-level condition, rubber shear spring assemblies on the low side of the frame are compressed and the rubber shear spring assemblies on the high side of the frame are tensioned.
The forces exerted by the rubber shear spring assemblies tend to maintain a true plane of vibrating motion for the frame, thereby reducing the likelihood of structural damage to the frame which can occur from twisting caused by non-planar vibratory motion. In addition, steel coil springs which connect the frame to a base do not handle lateral loading well. Over time coil springs which are laterally loaded will wear unevenly. The rubber shear spring assemblies of the present invention reduce lateral forces on the coil springs resulting from an out of level condition of the base, thereby increasing the life of the coil springs.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.